The present invention relates to a sensor unit which is suitable for use in a multiple sensor unit array of a main body unit for an optical fiber type photoelectric sensor, a proximate sensor having a separate sensor head, an ultrasonic sensor having a separate sensor head or the like, and in particular to a sensor unit which is suitable for performing a bi-directional optical data communication between the adjacent sensor units.
Various sensors such as photoelectric sensors, proximate sensors and ultrasonic sensors are used for detecting the presence or position of an object as a part of factory automation (FA). In particular, optical fiber type photoelectric sensors that have separate sensor heads are widely used in compact and high-density machines which are required to be controlled because such sensors can be mounted in a limited space. The term xe2x80x9csensorxe2x80x9d as used herein includes those producing a switching output by comparing a detected value with a threshold value as well as those for producing the detected value as an analog or a digital value.
In the case of a sensor having a separate sensor head as is the case with an optical fiber type photoelectric sensor, the sensor head and the main body unit are joined by a cable (consisting of an optical fiber cable in the case of a photoelectric sensor, or an electric cable in the case of a proximate sensor or an ultrasonic sensor). The main body unit is sometimes called as an amplifier unit in the industry. The main body unit is called in the following description as a xe2x80x9csensor unitxe2x80x9d.
The housing of a sensor unit accommodates various circuits such as a drive circuit for driving a sensor head and a signal processing circuits for processing the signal from the sensor head and generating an output signal of a desired form. In other words, the sensor unit housing accommodates a sensing circuit system which achieves a desired sensing function in cooperation with the sensor head.
Conventionally, sensor units for use in a multiple sensor unit array have been developed with the aim to accommodate a large number of sensor units in a console board or the like. Such a sensor system incorporating a large number of sensor units closely one next to another is illustrated in FIG. 14. The illustrated sensor units each consist of a main body unit (often called as an amplifier unit) of an optical fiber type photoelectric sensor.
As shown in the drawing, this sensor system comprises a DIN rail 301 placed inside a control console or the like, and a plurality of sensor units 300, 300, . . . which are adapted to be used in a multiple sensor unit array and mounted on the DIN rail 301 closely one next to another. In other words, each sensor unit 300 is mounted on the DIN rail 301 in alignment with other sensor units by fitting a DIN rail mount groove 302 formed in the bottom surface of the housing onto the DIN rail 301.
A pair of optical fiber cables consisting of an outgoing optical fiber cable 303 and an incoming optical fiber cable 304 extend from the rear surface of the housing of each sensor unit 300, and the free ends of these optical fiber cables 303 and 304 are connected to sensor heads 303a and 304a which are placed in a detection region.
An electric cable (or cord) 305 extends from the front surface of the sensor unit 300 to produce a switching output or a signal indicating the intensity of the received light which is generated by the sensing circuit system (not shown in the drawing) inside the unit housing. This electric cable 305 is connected to external control equipment such as a programmable logic controller (PLC) which is not shown in the drawing.
As the presence or position of an object is detected by the sensor heads 303a and 304a of the optical fiber cables 303 and 304 according to the change in the transmitted or reflected light, by virtue of the prescribed operation of the sensing circuit system of the sensor unit 300, a detection signal (a switching output or a signal indicating the intensity of the received light) is forwarded to control equipment such as a programmable logic controller (PLC) via the cable 305.
Thus, according to the sensor system described above, because the outer profile of the housing of each sensor unit 300 has a flat configuration with its small side aligned with the direction of the array, and is provided with a DIN rail mount groove 302 in its bottom surface, if the control console is provided with a DIN rail 301, a large number of such independent sensor units 300 can be mounted on the DIN rail 301 closely one next to another in a highly compact fashion.
In recent years, the sensing circuit system incorporated in the sensor unit is given with a progressively higher functionality and performance so that the sensor unit may be adapted to a greater variety of objects and a wider range of detecting conditions. Therefore, there is a growing need to set up the conditions for a larger number of data items for each sensor unit and to monitor the sensor unit to place the sensor unit in an optimum condition for detecting a greater variety of objects and a wider range of detecting conditions.
Such set-up work has been conventionally performed manually by manipulating small set-up keys provided on outer surface of each sensor unit housing while viewing a display unit which is typically difficult to read. Therefore, such work has been known to be irritating and time-consuming.
The sensor unit housing is made smaller and smaller because of the growing demand for more compact design. This trend severely hampers the effort to solve the problems associated with the inconvenience in manipulating the set-up keys on the sensor unit housing and the difficulty in reading the display on the sensor unit.
The inventors have conducted a research to the end of eliminating such problems of the prior art, and have conceived the idea that if each pair of adjacent sensor units in a sensor unit array can transfer data between them in both directions, it will become possible to provide a data set-up unit of good manipulability at an end of the sensor unit array which is easily accessible, and to transfer the data from the data set-up unit to each sensor unit. Also, it will become possible to transfer the data of each sensor unit to the sensor unit at an end of the array so that the data may be monitored on a data display device which provides a favorable visibility.
Implementation of such an idea requires an arrangement which allows a bi-directional data transfer between each pair of adjacent sensor units. However, in the technical field of sensor systems, no appropriate prior art is available that serves this purpose.
For instance, Japanese patent laid open publication (kokai) No. 9-64712 discloses a detection switch system in which a female connector and a male connector are provided on opposing surfaces of each pair of adjacent detection switches (which correspond to the sensor units of the present invention), and are joined together electrically so that the control circuit board of each detection switch may be supplied with electric power for the adjacent detection switch, and the light emission timing may be suitably varied from one detection switch to another by passing an external synchronization signal from the upstream detection switch to the downstream detection switch with a suitable time delay.
However, to achieve such a bi-directional data transfer system contemplated by the inventors, it is necessary to arrange a large number of sensor units, typically from 16 to 64 sensor units, in a series. Therefore, when a contact type connector is used for signal transfer means between each pair of adjacent sensor units as shown in the above publication, the signal transmission path contains so many contact points which may become faulty that such an arrangement would be too unreliable for any practical purpose.
Because the synchronization signal in this prior patent publication is intended for delaying the timing of light emission, the transfer of data takes place only in one direction, and this prior art is therefore based on a concept which is fundamentally different from that of the bi-directional data transfer contemplated by the inventors.
Also, the contact type connector disclosed in this prior patent publication requires a projection and a recess to be provided on either side surface of the sensor unit housing, and this not only necessitates a higher precision for the metallic die assembly for molding the sensor unit housing but also causes some inconvenience in stocking and packaging the parts of sensor unit. Because the connector involves a male and female engagement, when any particular sensor unit has become faulty and is required to be replaced, it is not possible to remove only the faulty sensor unit from the DIN rail, and the maintenance work such as replacing a sensor unit tends to require an excessive amount of work.
This invention was made in view of such problems of the prior art, and its primary object is to provide a sensor unit which allows a reliable bi-directional data transfer between each pair of adjacent sensor units in a sensor system using an array of sensor units.
Another object of the present invention is to provide a sensor unit which allows a reliable bi-direction data transfer between each pair of adjacent sensor units, and has flat housing side surfaces so that each sensor unit may be replaced without being interfered by the adjacent sensor units, and the manufacturing cost may be reduced through simplification of the design of the metallic molding die assembly.
Yet another object of the present invention is to provide a sensor unit which allows a reliable bi-directional data transfer between each pair of adjacent sensor units in a sensor system using an array of sensor units so that more enhanced data set-up manipulation and monitoring may be enabled through integration of various functions in each sensor unit.
Other objects and advantages of the present invention will become apparent to a person skilled in the art from the following description.
The sensor unit of the present invention is provided with a housing that allows a number of such sensor units to be arranged closely one next to another, and is adapted to be connected to a sensor head via a cable.
The xe2x80x9ccablexe2x80x9d as used herein means an optical fiber cable in the case of a photoelectric sensor, and an electric cable (cord) in the case of a proximate sensor or an ultrasonic sensor. The arrangement for mounting a number of sensor units is not limited to the one using a DIN rail, but may consist of any means or structure for mounting a number of sensor units.
The housing accommodates a sensing circuit system, and first and second optical communication circuits.
The sensing circuit system performs the desired sensing function in cooperation with the sensor head. The xe2x80x9cdesired sensing functionxe2x80x9d as used herein may vary depending on the kind of the sensor unit (photoelectric sensor, proximate sensor, ultrasonic sensor, and so on).
For instance, when the sensor unit consists of a photoelectric sensor, the sensing function consists of a photoelectric detecting function of either transmission or reflection type using a detection medium consisting of a detection light beam (of visible light, infrared light or the like). When the sensor unit consists of a proximate sensor, the sensing function consists of an object detecting function which is based on the change in properties such as the oscillation amplitude and oscillation frequency of an internal oscillation circuit due to the presence of an object in proximity. When the sensor unit consists of an ultrasonic sensor, the desired sensing function consists of an object detection function based on the use of a detection medium consisting of ultrasonic sound.
The xe2x80x9csensing circuit systemxe2x80x9d as used herein includes not only hardware for achieving the desired sensing function but also software which operates a microprocessor so as to perform specific functions.
The first optical communication circuit system comprises a light emitting device and a light receiving device for conducting a bi-directional communication with one of the adjacent sensor units when a plurality of such sensor units are arranged closely one next to another. Likewise, the second optical communication circuit system comprises a light emitting device and a light receiving device for conducting a bi-directional communication with the other of the adjacent sensor units when a plurality of such sensor units are arranged closely one next to another.
The xe2x80x9cbi-directional optical communicationxe2x80x9d as used herein means that not only transmission but also reception is enabled. It however does not matter if the bi-directional optical communication is conducted in full duplex mode or half duplex mode.
The first and second optical communication circuit systems each include not only a light emitting device such as a light emitting diode and a light receiving device such as a photodiode but also various other electric components that are required for optical communication such as software for transmission, a parallel/serial conversion circuit, a light emitting device drive circuit, a light receiving device output amplifier circuit, a serial/parallel conversion circuit and software for reception.
The term xe2x80x9coptical communication circuit systemxe2x80x9d is used herein to distinguish from the xe2x80x9csensing circuit systemxe2x80x9d. The structure of the optical signal transmission path between the light emitting device and light receiving device within the sensor housing can be freely selected. Light guiding means such as optical fiber cables, prisms and mirrors may be used to form all of or a part of the optical path between the light emitting device and light receiving device.
According to this structure, a bi-directional optical communication is enabled between each pair of adjacent sensor units in an array of sensor units, and as there is no need for a connector relying on a physical contact for transmission of signals between the adjacent sensor units, a high level of reliability can be ensured even when a large number of sensor units are arranged in an array for signal transfer.
According to a preferred embodiment of the present invention, the housing is provided with a first optical communication window provided on one side thereof for conducting an optical bi-directional communication with one of the adjacent sensor units in the sensor unit array, a second optical communication window provided on the other side thereof for conducting an optical bi-directional communication with the other of the adjacent sensor units in the sensor unit array, whereby the sensor unit is enabled to conduct an optical bi-directional communication with each of the adjacent sensor units in the sensor unit array via a corresponding one of the optical communication windows.
According to this structure, because the optical communication between each pair of adjacent sensor units is accomplished via the optical communication windows, the sides of the housing may consist of flat surfaces so that a significant cost reduction can be accomplished owing to the simplification of the metallic die assembly for molding the housing, and the simplification of the stocking and packaging of the sensor unit. Furthermore, when an array of such sensor units are mounted on a DIN rail closely one next to another, there is no mechanical interference between adjacent sensor units, and the work required in replacing one of the sensor units is simplified.
The optical communication window provided on each side of the housing may be fitted with a visible light cut-off filter, an optical lens or the like. Such a structure improves the efficiency in emission and reception of light and reduces noises in the optical communication by the light emitting device and light receiving device so that the tolerance in the relative positioning of adjacent sensor units is increased, and the reliability of the optical communication is improved.
The optical lens provided in the optical communication window on each side of the housing may consist of a semi-cylindrical lens having a flat surface facing outward and shared by the light emitting device and light receiving device, the light emitting device and light receiving device being arranged along an axial direction of the semi-cylindrical lens, and being reversed in position from one side of the housing to the other so as to complementarily oppose the counterparts thereof in the corresponding adjacent sensor unit in the sensor unit array.
According to this arrangement, because the single optical lens can be used for both emission and reception of light, the optical system can be simplified in structure, the work required in aligning the optical center lines is simplified, and a cost reduction can be accomplished.
The sensor unit of the present invention may further comprise data transfer control means for enabling a bi-directional transfer of data between each pair of adjacent sensor units in the manner of a bucket brigade by controlling the first and second optical communication circuit systems.
According to this structure, by passing the data received from one of the adjacent sensor units to the other adjacent sensor unit, a quick data transfer from one sensor unit to another can be accomplished.
As can be readily appreciated, the sensor unit of the present invention may consist of a photoelectric sensor, a proximate sensor or an ultrasonic sensor by appropriately designing the sensing circuit system.
A sensor system of the present invention incorporating a sensor unit array consisting of a large number of such sensor units has a novel structure, and provides novel advantages.
Specifically, according to the sensor system of the present invention, because a bi-directional exchange of signals between adjacent sensor units is enabled, it is possible to monitor a large number of sensor units or arbitrarily selected sensor units with a simple operation, in particular without requiring to individually operate the associated sensor units, by forwarding a monitor request command to the particular sensor units from an end of the sensor unit array via the intervening sensor units to be executed by the associated sensor units, and having responses therefrom returned to the source of the request command or the sensor unit at the end of the sensor unit array.
In a similar fashion, by replacing the monitor request command with a data setting command, setting of data to a large number of sensor units or arbitrarily selected sensor units can be executed with a simple operation, instead of individually operating the associated sensor units.